Method and rolling stand for cold rolling rolled stock

ABSTRACT

The invention relates to a method and a rolling stand ( 100 ) for cold rolling rolled stock. The rolling stand ( 100 ) comprises at least one upper and one lower backup roll ( 110 - 1, 110 - 2 ) and also an upper and a lower work roll ( 120 - 1, 120 - 2 ), which define a roll gap ( 128 ). Optionally, a lower and an upper intermediate roll ( 130 - 1, 130 - 2 ) may also be provided between the work rolls and the backup rolls. In order to ensure an absolutely equal circumferential speed of the upper and lower work rolls when cold rolling in skin-pass mode, it is proposed according to the invention to decouple the upper or lower work roll from its associated drive device.

The present invention relates to a method and a rolling stand for cold rolling rolled stock. The rolling stand comprises at least an upper and a lower backup roll and also an upper and a lower work roll, which define a roll gap. Optionally, a lower and an upper intermediate roll may also be provided between the work rolls and the backup rolls. Apart from the method, the present invention also relates to the said rolling stand.

Rolling stands and methods for their operation are principally known in the prior art, for example from EP 1 318 879 B1, DE 4417274 C2, EP 1 420 898 or from DE 4417274. Regarding the topic of coolant or lubricant application during cold rolling of the rolled stock moreover, reference is made to the following literature: DE 19744503 A1, EP 1 173 295, DE 10 2004 025058, EP 1 399 277 and DE 10 2007 0324857 (=WO 2008/071277), JP 620688613 A and Selzer, H., Entwicklungen im Kaltwalzbereich, Kaltwalz—Symposium der SMS Siemag AG (Developments in Cold Rolling Field, Cold Rolling-Symposium of SMS Siemag AG), Hilchenbach-Dahlbruch, Del., 16-17 Feb., 2000.

The prior art basically differentiates between reducing roll stands and rerolling stands.

The purpose of reducing roll stands is to reduce the rolled stock thickness by 30 to 80% per rolling pass. High rolling forces and rolling moments arise at these high levels of reduction. That is why highly effective roller cooling is needed. In this context, up to 10,000 L/min. of coolant volume is recirculated per rolling stand. The work rolls in the reducing roll stand a have relatively smooth surface without special texturing. During reducing operation, the upper backup roll rests on the upper intermediate roll and this in turn rests on the upper work roll. In the absence of an intermediate roll, such as in a four-roll stand, the upper backup roll then rests directly on the upper work roll. The rolling forces are in the range of 10 to 20 MN. The rolling moments are in the range of 100 to 200 kNm. During reduction, a special thickness control is deployed, which can be operated both in positioning control mode as well as in rolling force mode. During reduction, an essential actuating mechanism of the thickness control are almost exclusively the adjusting cylinders of the backup rolls, and the strip tension only in edge areas.

Reducing roll stands can have a six-roll or four-roll design, i.e. they can be designed with six or with four rolls. During reducing operation, both work rolls are typically rotationally driven to transfer a rolling moment onto both work rolls. Such type of reducing roll stands are known both for reducing of ferrous metal as well as for reducing of nonferrous metal. The unique noteworthy difference between operating the reducing stands for ferrous metal and nonferrous metal is in the use of the particular suitable cooling lubricant; the cooling lubricant is one medium which has both cooling and lubricating functions. Rolling oil is typically used as cooling lubricant for nonferrous metal, in particular for aluminum.

Besides the straight reducing stands for ferrous metal and nonferrous metal just described also straight rerolling stands are known, however only for ferrous metal. The purpose of rerolling stands is the embossing of texture onto the rolled stock to improve the strip flatness and/or improve the material characteristics of the rolled stock, e.g. to eliminate Lüders' bands or to adjust specific strengths. For this reason, the typically smooth work rolls with a surface roughened in a predetermined manner for embossing the texture onto the rolled stock, special skin-pass rolls are used. During skin-pass rolling only a single rolling pass with a rolled stock thickness reduction of 0.3 to 10% is typically performed. Embossing the texture creates material attrition, so-called metal flash, which interferes during further processing and heavily contaminates the dressing medium. During skin-pass rolling, the rolling force and the rolling moment are very low compared to reducing operation; during skin-pass rolling the rolling forces are specifically in a range between 1 to 4 MN. The rolling moments are typically in a range of 0 to 20 kNm. The quantity of approximately 20 L/min. of skin-pass rolling medium applied per side of rolled stock is at a significantly lower level when compared to reducing operation. The primary purpose of the dressing medium is essentially the cleaning of the rolled stock or of the rollers. Typically, neither of the two work rolls is driven in skin-pass mode; instead, merely the lower backup roll is driven and consequently a rolling moment is transferred to said work rolls. During the skin-pass mode the rolling force can either be applied via the adjusting cylinders of the upper backup roll; this is, however, on the condition that the upper backup roll bears on either the upper work roll or, if available, on the upper intermediate roll. As an additional alternative, the upper backup roll can also be lifted off the upper work roll or, if available, off the upper intermediate roll. After that the rolling force is applied during skin-pass mode by means of a suitable adjustment of the upper bending cylinders, which act either on the upper work roll or, if available, on the upper intermediate roll. In addition to the just described straight reducing stands and straight rerolling stands, there are also combination stands which can be operated both in reducing operation as well as in skin-pass mode, however only for ferrous metal and not for nonferrous metal.

The known straight reducing roll stands for nonferrous metal are unsuitable for combined operation, i.e. for alternative skin-pass mode for nonferrous metal, because the reducing roll stands are designed for rolling forces that would be excessive for a skin-pass mode for nonferrous metal. The frictional forces within the hydraulic adjustment are approximately proportional to maximum force, i.e. an adjusting cylinder that was designed for high forces cannot function with the necessary required accuracy at low rolling forces because of its internal friction.

In reducing roll stands normally two rolls, as a rule the work rolls, are driven in order to transfer the required rolling moment preferably uniformly into the roll gap. Smallest differences in diameter between the work rolls produce moment differences between the rolls which are not harmful for the rolling results however, because the high reductions are compensated in the rolled stock by shear effects, for example. During skin-pass mode with small reductions/skin-pass levels this internal compensation cannot take place because transformations take place only close to the rolled stock surface. The rolling moments are moreover so small that the drive from only one roll is sufficient.

Based on this prior art, the object of the present invention is to develop a known method and a known rolling stand that can be operated optionally in reducing operation or skin-pass mode to the extent that the quality of the rolled stock and the stability of the rolling conditions in the skin-pass mode are improved.

This object is accomplished by the method claimed in claim 1. This method is characterized in that the upper or the lower work roll is disconnected from its drive unit in skin-pass mode. Neither the upper nor the lower backup roll are driven during the skin-pass mode according to the present invention.

Within the scope of the present invention, the term “or” is to be interpreted as exclusive alternative. A simultaneous disconnection of both work rolls in skin-pass mode, as known in the prior art, is expressly not meant and is excluded from the scope of the patent.

Aside from the drive concept for the work rolls in skin-pass mode, the definitions of reducing operation and skin-pass mode stated at the outset hold true for the subject matter of the present invention. However, for the drive of the work rolls in skin-pass mode, the claimed drive concept is valid.

The claimed method provides that for a significant reduction of the rolled stock thickness the rolling stand can also be operated in a reducing operation operating mode alternatively to the skin-pass mode. Such a combination stand, which facilitates skin-pass rolling of ferrous metal and nonferrous metal and reducing of ferrous metal and nonferrous metal on one stand, offers distinct advantages in particular from a financial perspective compared with two separate stands, i.e. one reducing roll stand and one separate rerolling stand.

Smallest differences in diameter on the two work rolls, such as can occur because of grinding defects or varying thermal expansion for example and which resulted in speed differences on the two work rolls, are advantageously prevented by the claimed drive concept in which the two work rolls are respectively rotationally coupled on the rolled stock by means of frictional contact. Even changes in moment trimming, chatter, surface defects and/or unstable rolling conditions, as they typically develop during forced coupling of both work rolls onto the pinion stand gear drive, are advantageously prevented by the claimed drive of only one of the two work rolls. In the aggregate, the overall quality of the rolled stock is improved in skin-pass mode by the claimed drive concept and the rolling conditions are stabilized. The claimed method is therefore also particularly suitable for skin-pass rolling of nonferrous metal strip.

According to a first exemplary embodiment of the method according to the present invention, during skin-pass mode the upper backup roll is lifted off the upper work roll, or, if present, off the upper intermediate roll, and the application and the adjustment of the rolling force results from the action of the upper bending cylinders on the upper work roll, or, if present, on the upper intermediate roll.

The flux of force in the rolling stand and the shaping of the components are essential for the elastic behavior of the rolling stand. Clearances and lash are therefore to be avoided, because free movement of the very heavy components would result in damage within a short period. For this reason, all joints between moving components, such e.g. between superimposed bearing housings, i.e. chocks, of adjacent rollers are balanced, i.e. preloaded, by using hydraulic adjustment. A backup roll can weigh up to 200 t. This corresponds to a necessary force of 2 MN. This corresponds to the same magnitude as the required rolling force in skin-pass mode. If an adjustment of the backup rolls by means of their adjusting cylinders were still be provided additionally, the rolling force acting on the rolled stock would very quickly exceed the smaller skin-pass forces necessary in skin-pass mode. Moreover, the (smaller) skin-pass forces could no longer be controlled properly, because the gravitational force alone of the backup roll is in the same order of magnitude.

The lifting of the upper backup roll off the upper work roll or off the upper intermediate roll provided according to the first exemplary embodiment therefore prevents the described problem of the excessive rolling force, if the backup roll is supported.

Potential side effects of raising the backup roll, such as a possible change of the roll gap profile, are redressed by the application and the adjustment of the rolling force by the action of the upper bending cylinders on the upper work roll or, if available, on the upper intermediate roll, as claimed.

Within the scope of the present invention, the upper backup roll can in principle also remain resting on the upper work roll or on the upper intermediate roll during the skin-pass mode; however, then the said disadvantages persist during the fine adjustment of the skin-pass forces.

According to a further exemplary embodiment, the method according to the present invention provides that the thickness of the rolled stock in skin-pass mode is adjusted to a predetermined constant target thickness with the aid of a skin-pass level control circuit, e.g. by suitable variation of the strip tension of the rolled stock or of the rolled stock speed, as manipulated variables. A prerequisite of the skin-pass level control, i.e. the thickness control during skin-pass rolling, is that the rolling force must be kept constant to maintain uniform embossing of the skin-pass roll roughness onto the strip. Preferably, no sudden changes in thickness must arise. For this purpose, the method according to the present invention advantageously provides controlling the rolling force applied on the rolled stock by using a rolling force control circuit, wherein the bending cylinders serve as actuators for the rolling force. Alternatively or additionally, a position control circuit is preferably provided to keep the adjustment status of the work rolls constant.

Both the rolling force control as well as the position control must be in real time if possible, which is why the step responses of the two control circuits must preferably less than 80 ms.

According to a further exemplary embodiment, the method according to the present invention optionally provides that a flatness control circuit can also be provided for controlling the flatness of the rolled stock. The flatness control circuit then comprises a flatness measuring device, e.g. a flatness measuring wheel on the rolling stand outlet for recording the actual flatness of the rolled stock. Such measured actual flatness is compared with a predetermined target flatness, i.e. the difference between these two flatnesses is formed and this difference is provided as a flatness control deviation to a flatness controller, which in accordance with the flatness control deviation generates a suitable actuating signal for an actuating mechanism, for example the upper bending cylinders of the upper intermediate or work roll. The bending cylinders are controlled in this manner such that the flatness at the outlet of the rolling stand ideally corresponds to the predetermined target flatness.

According to a further exemplary embodiment of the present invention, the lubricant is recirculated and after use is prefiltered prior to its reuse or its recirculation. During its pre-filtration, potential metal flash particles that could be generated during the skin-pass mode are removed from the lubricant. Preferably, the lubricant will be prefiltered already prior to microfiltration, which is typically done anyway.

According to a further exemplary embodiment it is provided that only a minimal quantity of pure lubricant is used in skin-pass mode. Regarding the minimum quantity, the involved quantity used is ideally small enough so that it is completely consumed in the roll gap during the skin-pass mode, so that at the rolling stand discharge point no lubricant remains on the rolled stock surface and no lubricant drains laterally from the rolled stock. In principle, this minimal quantity lubrication process is an alternative to the lubricant recirculation as described in the previous paragraph. If during the minimum quantity lubrication process small residual lubricant quantities in fact still remain on the rolled stock, these residual quantities can naturally be fed into recirculation anyhow for reuse after prefiltration.

The method according to the present invention is provided for nonferrous metal strip or ferrous metal strip as rolled stock. During skin-pass rolling of nonferrous metal strip as rolled stock, preferably rolling oil is used as lubricant by utilizing its lubricant function. Fundamentally, lubricant oil can be used in all operating modes, however, that is both for reducing of nonferrous metal strip or nonferrous metal strip and also for skin-pass rolling of nonferrous metal strip or ferrous metal strip.

In the skin-pass mode according to the present invention, typically skin-pass rolls with a specific surface roughness are used as work rolls. These skin-pass rolls are preferably cleaned by high-pressure spraying with the lubricant, or by using brushes during work breaks in the skin-pass mode. The cleaning process offers the advantage of increasing the service life of the skin-pass rolls roughened specially for the skin-pass process.

The abovementioned problem is furthermore solved by a rolling stand pursuant to claim 11. This solution is characterized in that the torque transfer device has at least one coupling device and one associated control unit for disconnecting the upper or the lower work roll from the at least one drive unit during the skin-pass mode. The advantages of this solution correspond to the above cited advantages with reference to the described method.

Further advantageous embodiments of the method according to the present invention and the rolling stand according to the present invention are subject of the dependent claims.

In total three figures are attached to the specification, wherein

FIG. 1 illustrates a four-roll rolling stand designed according to the present invention;

FIG. 2 illustrates a six-roll rolling stand designed according to the present invention; and

FIG. 3 illustrates the method according to the present invention for adjusting a reducing mode or skin-pass mode on a combination stand.

The present invention is subsequently described in detail with reference to the said figures in the form of exemplary embodiments. In all figures, identical technical components are designated with identical reference symbols.

FIG. 1 illustrates a four-roll rolling stand 100. The rolling stand specifically comprises an upper work roll 120-1, a lower work roll 120-2 as well as an upper backup roll 110-1 and a lower backup roll 110-2. The work rolls are arranged between the two backup rolls. During rolling operation, the two work rolls define a roll gap 128 for cold rolling rolled stock passing between them.

On the feed side of the rolling stand, spray bars 195 for application of coolant and lubricant onto the work rolls 120-1 are arranged at the level of the upper and lower work rolls 120-1, 120-2.

A thickness control circuit 150, a rolling force control circuit 160, a position control circuit 170 and/or a flatness control circuit 180, is assigned to the rolling stand 100.

Furthermore, a lubricant circulation system and coolant circulation system is assigned to the rolling stand 100, said circuit comprising devices for collection of the coolant or lubricant draining from the rollers for filtering the used coolant or lubricant and for recycling the purified coolant or lubricant in particular to the work rolls. Typically, a recirculation system 192 is used for recycling. A microfilter 194 is typically used for the purification or filtration of the coolant and/or lubricant. According to the present invention, an additional pre-filter 190 is provided upstream of this microfilter however for filtering out metal flash from the coolant or lubricant, such as arises during skin-pass rolling of rolled stock. As illustrated in FIG. 1, this pre-filter 190 can be positioned either upstream or downstream of a recirculation system 192; however, in all cases said pre-filter is arranged upstream of the microfilter 194 in the direction of flow.

In addition to the just described recirculation of the lubricant, a minimal quantity lubrication process can also take place, during which only sufficient lubricant is applied onto the rolled stock on the feed side and/or onto the work rolls as will actually be used or needed in the roll gap during rolling

The work rolls 120-1, 120-2 are driven by at least one drive unit 124, 124-1, 124-2 by interposing a torque transfer device 120′, 120″.

In a first embodiment, as it is illustrated in FIG. 1, the torque transfer device 120′ has an upper coupling device 126-1, an upper drive spindle 122-1 and optionally an upper transmission gear for transfer of a torque from the upper drive unit 124-1 to the upper work roll 120-1. For this purpose the upper drive spindle 122-1 is arranged between the upper work roll and the upper drive unit 124-1, and the optional transmission gear to 129-1 is arranged between the upper drive spindle and the upper drive unit. The upper coupling device 126-1 can be arranged between the upper work roll and the upper drive spindle and/or between the upper drive spindle and the upper transmission gear and/or between the upper transmission gear and the upper drive unit, and/or it is designed as no-load position of the upper transmission gear.

According to its first embodiment, the torque transfer device 120′ comprises a lower coupling device 126-2, a lower drive spindle 122-2 and optionally a lower transmission gear 129-2 for transferring a torque from the lower drive unit 124-2 to the lower work roll 120-2. For this purpose, the upper drive spindle 122-2 is arranged between the lower work roll and the upper drive unit 124-2 and the optional lower transmission gear 129-2 between the lower drive spindle and the lower drive unit. The lower coupling device 126-2 can be arranged between the lower work roll and the lower drive spindle and/or between the lower drive spindle and the lower transmission gear and/or between the lower transmission gear and the lower drive unit, and/or it is designed as no-load position of the lower transmission gear.

In FIG. 1, an example of the upper coupling device is shown in the open, i.e. the disengaged state, while the lower coupling device is shown in the closed, i.e. the engaged state.

The moment flow from the drive units 124, 124-1, 124-2 to the work rolls can be optionally interrupted using the coupling devices. For the coupling device, positive, frictional, magnetic or fluid dynamic modes of action are conceivable. The actuation of the switchable coupling device can have a mechanical, electrical, electromagnetic, pneumatic or any other design. The switchable coupling device can be configured on or in the pinion stand gear drive, within the spindle, or on the roll neck.

The four-roll rolling stand 100 can be operated in a skin-pass mode of operation; the associated configuration of the rolling stand 100 is illustrated schematically in FIG. 1. The two backup rolls 110-1, 110-2 are not driven in the skin-pass mode.

Furthermore, upper bending cylinders 140 can be recognized in FIG. 1, which act on the upper work roll 120-1 on the drive side AS and on the operator side BS. If rolled stock is present in the roll gap 128 and the two bending cylinders 140 respectively exert half a bending force F/2 onto the upper work roll 120-1, this action of the bending force results in negative bending of the upper work roll.

In skin-pass mode, the upper backup roll 110-1 is initially lifted-off the upper work roll 120-1. This has the advantage that the rolling force acting on the rolled stock in the roll gap 128, insofar as it is determined by the gravitational force of the supported rolls, is significantly less with a lifted-off upper backup roll than if the upper backup roll were supported on the upper work roll and would therefore rest on the rolled stock. The rolling force, which in skin-pass mode is significantly smaller compared to reducing operation, is expressly desirable in skin-pass mode, because in skin-pass mode the emphasis is not on the thickness reduction but merely on embossing a surface roughness structure predetermined by the work rolls in form of skin-pass rolls onto the surface of the rolled stock.

Apart from the gravitational force of the upper work roll 120-1, the rolling force applied on the rolled stock in skin-pass mode is additionally determined respectively by half of the bending force applied additionally from the two bending cylinders 140 on the operator side BS and the drive side AS of the rolling stand. With the aid of the bending cylinders, an operating point for the total rolling force acting on the rolled stock can be defined and this rolling force can be kept constant or be corrected, if desired, using the assigned rolling force control circuit 160. If the bending cylinders 140 are used for the accurate adjustment of the rolling force in this manner, this is also referred to as expanded bending system.

A particular distinctive mark of the skin-pass mode according to the present invention moreover is that neither of the two backup rolls 110-1, 110-2 and also only one of the two work rolls 120-1, 120-2 is driven. An example of this is the lower work roll 120-2 in FIG. 1. Said lower work roll is coupled by means of the closed lower coupling device 126-2 and the lower drive shaft 122-2 and optionally by means of the transmission gear 129-2 onto the lower drive unit 124-2, while the upper work roll 120-2 is disconnected from the upper drive unit 124-1 assigned to it by means of the open upper coupling device 126-1.

As previously mentioned, the thickness reduction of the rolled stock is significantly less in skin-pass mode than in reducing operation. But thickness reduction can also take place during skin-pass mode, nevertheless; said thickness reduction is then typically referred to as skin-pass level control and is performed using a skin-pass level control circuit 150. The skin-pass level control circuit controls the thickness reduction of the rolled stock during the skin-pass mode to a predetermined constant target thickness by suitable variation of the strip tension of the rolled stock or by suitable variation of the rolling speed. The strip tension or the rolling speed serve as manipulated variables for the skin-pass level control.

Alternatively or additionally to the rolling force control circuit, a position control circuit 170 can be assigned to the rolling stand for keeping the adjusting position of the work rolls constant. This can be recorded either directly or indirectly metrologically by evaluation of the positions of the bending cylinders 140 and be controlled by means of the bending cylinders as actuating mechanisms. Both the control of the rolling force as well as the control of the position of the work rolls will preferably take place in real time. For this purpose, the respective control circuits must be correspondingly quick; preferably, their step responses are shorter than 80 ms.

Furthermore a flatness control circuit 180 for controlling the flatness of the rolled stock can be assigned to the rolling stand. The flatness control circuit 180 includes a measuring element 197, for example a flatness measuring wheel for recording the rolled stock at the rolling stand outlet and for recording the actual flatness of the rolled stock there. This measured actual flatness of the rolled stock is compared by subtraction with a predetermined target flatness and the flatness deviation resulting from the subtraction is evaluated by a flatness controller, which in accordance with the flatness control deviation outputs a control signal to the actuating mechanisms, for example to the upper negative-acting bending cylinders 140, for controlling the flatness to the predetermined target flatness.

In principle, only a minimal lubricant quantity is used in skin-pass mode. In other words, only sufficient lubricant is used as is actually consumed or required in the roll gap; ideally, no lubricant flows off laterally from the rolled stock, in particular during the skin-pass mode, and ideally also no lubricant remains on the rolled stock after it has passed through the roll gap.

The rolling stand is designed either for cold rolling of ferrous metal strip or of nonferrous metal strip. During cold rolling of nonferrous metal strip, so-called rolling oil or also a water/oil mixture is used as cooling lubricant.

The rolling stand is designed as combination rolling stand, which can be operated either in a reducing operating mode or in a skin-pass mode.

FIG. 2, in contrast to FIG. 1, illustrates a six-roll rolling stand. This differs from the four-roll rolling stand shown in FIG. 1 by having an upper intermediate roll 130-1, which is arranged between the upper work roll and the upper backup roll, and a lower intermediate roll 130-2, which is arranged between the lower work roll and the lower backup roll. FIG. 2 illustrates the operation of this six-roll rolling stand in the skin-pass operating mode, in which the upper backup roll 110-1 is lifted off the upper intermediate roll 130-1. The upper bending cylinders 140 now do not act on the upper work roll 120-1, but on the upper intermediate roll 130-1. Other than that, the structure of the rolling stand and the functionality or method of operation of the rolling stand in skin-pass mode correspond to the data described above with reference to FIG. 1.

FIG. 2 illustrates a second embodiment of the torque transfer device 120″. Pursuant to this second embodiment, alongside the coupling device 126 the torque transfer device 120″ has an upper and a lower drive spindle 122-1, 122-2 as well as a pinion stand gear drive 129 for transferring a torque from the sole drive unit 124 to at least one of the work rolls 120-1, 120-2. The pinion stand gear drive is connected on its moment input with the sole drive unit 124. The upper drive spindle 122-1 is arranged between the upper work roll and the upper moment output of the pinion stand gear drive, the lower drive spindle 122-2 is arranged between the lower work roll and the lower moment output of the pinion stand gear drive, and the pinion stand gear drive 129 is arranged between the upper and the lower drive spindle and the drive unit 124. The coupling device 126 can be arranged between the upper work roll and the upper drive spindle and/or between the upper drive spindle and the pinion stand gear drive and/or between the lower work roll and the lower drive spindle and/or between the lower drive spindle and the pinion stand gear drive, or it is designed as no-load position of the pinion stand gear drive.

Pursuant to its first embodiment the torque transfer device 120′ can be operated not only in conjunction with a four-roll stand, as shown in FIG. 1, but also in conjunction with a six-roll stand. Pursuant to its second embodiment, the torque transfer device 120″ can be operated not only in conjunction with a six-roll stand, as shown in FIG. 2, but also in conjunction with a four-roll stand.

In both embodiments of the torque transfer device 120′, 120″, a control unit 127 is assigned to the coupling devices. The control unit makes it possible to open or close the coupling devices either in the reducing operating mode or in the skin-pass operating mode, depending on the rolling stand operation.

FIG. 3 finally illustrates the necessary process steps for selecting either the reducing operating mode or the skin-pass operating mode on a combination rolling stand which can run both operating modi alternatively.

When selecting the reducing operating mode, the stand parameters are initially adjusted to reducing operation. This means in particular that the technological control circuits, such as the thickness control circuit for which the recording of the rolling force and position of the adjustments are essential, as well as the flatness control circuit, for which the available actuating mechanisms are essential, are parameterized accordingly. The technological control circuits are activated both in skin-pass mode as well as in reducing operation, but are possibly parameterized differently.

The thickness control in reducing operation is typically in the form of a monitor or mass flow control. All rolls are integrated in the flux of force. The adjustment of the rolling force and of the position of the work rolls in reducing operation is by means of the adjusting cylinders, which act on the upper backup roll resting on the upper intermediate roll or on the upper work roll. If intermediate rolls are available, these are in contact with the work rolls. Accordingly, in reducing operation these adjusting cylinders must be operated as actuating mechanisms in the said control circuits.

In reducing operation, both work rolls are rotationally driven from the at least one drive unit 124, 124-1, 124-2 by means of the torque transfer device 120′, 120″. In reducing operation, rolls with a smooth surface are typically selected as work rolls. After completion of all said steps, the rolling stand is then essentially ready for rolling.

If the skin-pass operating mode is selected alternatively, then according to the present invention one of the two work rolls within the torque transfer device 120′, 120′ is uncoupled from the drive unit by means of the coupling device, while the other work roll remains to be coupled-up. Subsequently, it is then checked, whether the rolling force to be expected in skin-pass mode is greater or not than a predetermined rolling force threshold value F-Grenz. If this is not the case, the upper backup roll is lifted off the upper work roll or off the upper intermediate roll.

The rolling force circuit and the position control circuit are configured such that the upper bending cylinders 140 are controlled as actuating mechanisms. The thickness control in skin-pass mode is typically done as skin-pass level control. If the rolling force to be adjusted in skin-pass mode exceeds the predetermined threshold value, the upper backup roll is placed onto the upper work roll or onto the upper intermediate roll.

Finally, all stand parameters, in particular all target values for the control circuits activated in skin-pass mode are adjusted to suitable target values in the skin-pass mode. In skin-pass mode, the stand parameters are adjusted to ensure the definite feedthrough of the bending systems and the required stand rigidity parameters for the thickness control. These parameters differ significantly, depending on the selected mode of operation, but also in the selected form of application of the upper backup roll. In skin-pass mode, the work rolls used are typically special skin-pass rolls with a predetermined surface roughness.

In skin-pass mode, a minimal quantity lubrication process or alternatively a lubricant recirculation system with the pre-filter 190 can be provided to isolate the abraded particles (metal flash) from the lubricant in skin-pass mode and therefore relieve the load on the main filter. After completion of the said steps, the rolling stand is then essentially ready for rolling.

The combination rolling stand according to the present invention is designed suitable to be converted from the reducing configuration into the skin-pass configuration and vice versa. For this purpose, specifically in particular the upper backup roll, must optionally be placeable onto the upper work roll and be lifted off same, the upper and the lower work roll must be suitable for coupling and decoupling onto or from the drive unit either individually or as a pair, and the smooth reducing work rolls and the roughened skin-pass work rolls must be interchangeable. Optionally, also the prefilter for filtering of metal flash in skin-pass mode may be removable during conversion to reducing operation, because this prefilter can typically be dispensed with in reducing operation.

List of reference symbols 100 rolling stand 110-1 upper backup roll 110-1 lower backup roll 120′ torque transfer device according to first exemplary embodiment 1 upper coupling device 120″ torque transfer device according to second exemplary embodiment 2 lower coupling device 120-1 upper backup roll 120-2 lower backup roll 122-1 upper drive spindle for upper work roll 122-2 lower drive spindle for lower work roll 124 (sole) drive unit for pinion stand gear drive 124-1 upper drive unit for upper work roll 124-2 lower drive spindle for lower work roll 126 coupling device during use of pinion stand gear drive 127 control unit 128 roll gap 129 pinion stand gear drive 129-1 upper transmission gear 129-2 lower transmission gear 130-1 upper intermediate roll 130-2 lower intermediate roll 140 bending cylinder 150 thickness control circuit 160 rolling force control circuit 170 position control circuit 180 flatness control circuit 190 prefilter 192 recirculation system 194 microfilter 195 spray bar 197 measuring element 200 rolled stock AS drive side BS operator side F bending force 

1. A method for operation of a rolling stand (100) for cold rolling rolled stock (200), wherein the rolling stand comprises at least one upper and one lower backup roll (110-1, 110-2) and also an upper and a lower work roll (120-1, 120-2), which define a roll gap (128), and optionally also an upper and lower intermediate roll (130-1, 130-2), and wherein the rolling stand optionally can be operated in a reducing operation operating mode for reducing the thickness of the rolled stock (200) or in a skin-pass mode; characterized in that neither the upper back-up roll (110-1) nor the lower back-up roll (110-2) are driven during the skin-pass operation, and the upper or the lower work roll (120-1, 120-2) is decoupled from its drive unit (124, 124-1, 124-2).
 2. The method according to claim 1, characterized in that for the skin-pass mode the upper backup roll (110-1) is lifted off the upper work roll (120-1), or, if present, off the upper intermediate roll (130-1); and in that the application and the adjustment of a rolling force (F) ensues due to the action of upper bending cylinders (140) on the upper work roll (120-1), or, if present, on the upper intermediate roll (130-1).
 3. The method according to claim 2, characterized in that the thickness of the rolled stock (200) in skin-pass mode is adjusted to a predetermined constant target thickness with the aid of a skin-pass level control circuit (150), by suitable variation of the strip tension of the rolled stock or of the rolled stock speed as manipulated variables.
 4. The method according to claim 3, characterized in that the bending force (F) applied from the bending cylinders (140) onto the rolled stock (200) with the aid of a rolling force control circuit (160) and/or preferably also the adjusting position of the work rolls (120-1, 120-2) is/are kept constant with the aid of a position control circuit (170).
 5. The method according to claim 2, characterized in that the flatness of the rolled stock is controlled with the aid of a flatness control circuit (180) by measuring the actual flatness at the rolling stand outlet and by suitable action on actuating mechanisms in accordance with a flatness control deviation as difference between a predetermined target flatness and the measured actual flatness.
 6. The method according to claim 1, characterized in that the lubricant is prefiltered after its use and prior to its reuse.
 7. The method according to claim 1, characterized in that only a minimal quantity of pure lubricant is used in skin-pass mode.
 8. The method according to claim 1, characterized in that the rolled stock (200) involves nonferrous metal strip or ferrous metal strip.
 9. The method according to claim 8, characterized in that rolling oil is used as lubricant during skin-pass rolling of nonferrous metal strip as rolled stock.
 10. The method according to claim 1, characterized in that skin-pass rolls with surface roughening are used as work rolls (120-1, 120-2) in skin-pass mode; and that the skin-pass rolls are preferably cleaned by high-pressure spraying with a lubricant and/or with the aid of brushes during work breaks of the skin-pass mode.
 11. A rolling stand (100) for cold rolling rolled stock, comprising: one upper and one lower backup roll (110-1, 110-2); one upper and one lower work roll (120-1, 120-2), which are supported between the backup rolls and define a roll gap (128); optionally also one upper and one lower intermediate roll (130-1, 130-2) which are supported between the work rolls and backup rolls; at least one drive unit (124, 124-1, 124-2) for driving the work rolls; and one torque transfer device (120′, 120″) for transferring a torque from the at least one drive unit to the work rolls, wherein the rolling stand is designed as combined reducing roll stand and rerolling stand with the alternative reducing operating modi for the thickness of the rolled stock, or for skin-pass mode; characterized in that the torque transfer device (120′, 120″) comprises at least one coupling device (126, 126-1, 126-2) and one associated control unit (127) for decoupling the upper or the lower work roll from the at least one drive unit (124, 124-1, 124-2) during the skin-pass mode during which both back-up rolls (110-1, 110-2) are not being driven.
 12. The rolling stand (100) according to claim 11, characterized in that the drive unit for driving the upper work roll is provided in form of an upper drive unit (124-1); and the torque transfer device (120′) comprises the coupling device in form of an upper coupling device (126-1), one upper drive spindle (122-1) and optionally one upper transmission gear (129-1) for transfer of a torque from the upper drive unit (124-1) onto the upper work roll (120-1), wherein the upper drive spindle (122-1) is arranged between the upper work roll and the upper drive unit (124-1) and the optional transmission gear (129-1) is arranged between the upper drive spindle and the upper drive unit; and wherein the upper coupling device (126-1) is arranged between the upper work roll and the upper drive spindle and/or between the upper drive spindle and the upper transmission gear and/or between the upper transmission gear and the upper drive unit and/or is designed as no-load position of the upper transmission gear (129-1).
 13. The rolling stand (100) according to claim 12, characterized in that the drive unit alongside the upper drive unit (124-1) also comprises one lower drive unit (124-2) for driving the lower work roll (120-2); and the torque transfer device (120′) furthermore comprises one lower coupling device (126-1), one lower drive spindle (122-2) and optionally one lower transmission gear (129-2) for transfer of a torque from the lower drive unit (124-2) onto the lower work roll (120-2), wherein the lower drive spindle (122-2) is arranged between the lower work roll and the lower drive unit (124-2) and the optional lower transmission gear (129-2) is arranged between the lower drive spindle and the lower drive unit; and wherein the lower coupling device (126-2) is arranged between the lower work roll and the lower drive spindle and/or between the drive spindle and the lower transmission gear (129-2) and/or between the lower transmission gear and the lower drive unit (124-2) and/or is designed as no-load position of the lower transmission gear.
 14. The rolling stand according to claim 11, characterized in that the torque transfer device (120″) alongside the coupling device (126) comprises one upper and one lower drive spindle (122-1, 122-2) and a pinion stand gear drive (129) for transfer of a torque from the drive unit (124) onto at least one of the work rolls (120-1, 120-2), wherein the pinion stand gear drive is connected on its moment input with the sole drive unit (124); wherein the upper drive spindle (122-1) is arranged between the upper work roll and the upper moment output of the pinion stand gear drive, the lower drive spindle (122-2) is arranged between the lower work roll and the lower moment output of the pinion stand gear drive and the pinion stand gear drive is arranged between the drive spindles (122-1, 122-2) and the drive unit (124); and wherein the coupling device (126) is arranged between the upper work roll and the upper drive spindle and/or between the upper drive spindle and the upper moment output of the pinion stand gear drive and/or between the lower work roll and the lower drive spindle and/or between the lower drive spindle and the lower moment output of the pinion stand gear drive and/or is designed as no-load position of the pinion stand gear drive.
 15. The rolling stand (100) according to claim 11, characterized by at least upper bending cylinders (140) for application and adjustment of a rolling force (F) in the roll gap (128) by action on the upper work roll (120-1) or, if present, on the upper intermediate roll (130-1).
 16. The rolling stand (100) according to claim 11, characterized in that the rolling stand (100) comprises one skin-pass level control circuit (150) for controlling the thickness of the rolled stock in the skin-pass mode operational mode, one rolling force control circuit (160) for keeping the rolling force constant during the skin-pass mode, one position control circuit (170) and/or one flatness control circuit (180) for ensuring the flatness of the rolled stock.
 17. The rolling stand (100) according to claim 11, characterized in that the rolling stand (100) is designed to be operated pursuant to the method according to one of the claims 1 to
 10. 18. The rolling stand (100) according to claim 11, characterized by a spray bar (195) for rolling oil in the inlet of the rolling stand for skin-pass rolling of nonferrous metal strip as a rolled stock. 